Some Aspects of the Ontogeny of Cliff Nesting Behaviour in the Kittiwake (Rissa Tridactyla) and the Herring Gull (Lar Us Argentat Us)

Abstract

This study analyses the behavioural peculiarities that enable Kittiwakes to raise their young on narrow cliff ledges. For comparison parallel studies were made on both Cliff and ground nesting Herring Gulls and some aspects of the ontogeny of the behaviour involved were investigated. 1. The Nest Cup. Kittiwake chicks and to a lesser extent, cliff nesting Herring Gull chicks, rarely leave their nests. This is not because they lack mobility, as was shown by a number of experiments, nor is it consequent upon nest construction. My observations show that the chicks' safety is due to a complex of behavioural characteristics. 2. Parental Behaviour. Chicks are brooded continuously for the first day of life but after this the Herring Gull tends to brood spasmodically and far less frequently than the Kittiwake. Experiments showed that young chicks were not inhibited of moving in darkness but this tendency would probably be checked by parents brooding. Kittiwakes are loathe to leave their broods unguarded even during a disturbance or when incited to fight. Herring Gulls are more easily frightened into flying from their nests and readily leave their chicks to enjoin a fight. Kittiwakes always alight at the nest and feed their chicks from their throat. Herring Gulls feed theiti chicks anywhere on their territory and, particularly when a feeding call is given, chicks run to them. This behaviour endangers cliff nesting chicks, however they appear to learn, within their first week of life, not to attempt to approach a calling parent but to wait until it flies to the nest. 3. Chicks Behaviour in the Nest. Cliff nesting Herring Gull chicks behave very like Kittiwakes in that they rarely stand for long periods and their main orientation is toward the wall. But unlike Kittiwakes they are vulnerable whilst wing flapping because more than one chick may flap at a time. They are also more vulnerable when disturbed for although some 'freeze' others run and may jump off the ledge. 4. Chicks reaction to a Visual Cliff. The jumping of the Herring Gull occurs despite the fact that under less disturbing Conditions many show an avoidance of the cliff edge. But their response is not as dramatic as that shown by the Kittiwake chicks who give a perfect avoidance response. 5. Chicks reaction to a Tactile Cliff. The Kittiwakes showed a less perfect edge avoidance when elicited by tactile cues alone, and it was not certain that Herring Gull chicks could detect edges at all on tactile cues alone. 6. Chicks reaction to a Wall. Although all cliff nesting chicks orient toward a wall when in their nest, Herring Gull chicks did not appear to be attracted to a wall and only very young Kittiwake chicks were attracted to a wall which they would approach and snuggle against. 7. The ontogeny of some of the behaviour studied. Because chicks taken from the natural nest site might have already g-ained and profited from experience, eggs were hatched in an incubator and chicks raised under one of three conditions. One group were raised in a situation similar to ground nesting conditions, a second in cliff nest like conditions, whilst a third group were reared in perspex boxes, suspended above the ground, so that they had the visual stimuli of an abyss combined with the 'wrong' tactile stimuli. On the whole the Kittiwake chick's responses are remarkably independant of, and resistant against experience, for the full repertoire of responses studied were present in all these incubator hatched chicks, except the tactile anti-cliff response, which did not develop in one-day old chicks who had no experience of an edge. In the Herring Gull the story is somewhat different. Differences between cliff and ground nesting Herring Gulls must be due to their upbringing as was indicated both by observations on chicks from eggs that had been exchanged between cliff and ground breeding sites and from the laboratory experiments. Also their visual anti-cliff response which is less than perfect showed a phenotypic improvement in laboratory tests.